Tratamento do pó de capim elefante por explosão a vapor e impregnação de tensoativo para adsorção de cromo em meio aquoso: processos batelada e dinâmico

Abstract

Activities such as mining and tanning are the most polluting sources of heavy metals, generating toxic residues for the environment and human beings. Tanning is responsible for releasing trivalent chromium into the environment, which causes effects on the skin and, in high doses, can cause cancer. In this study, the adsorption capacity of trivalent chromium was evaluated using elephant grass (Pennisetum purpureum) as a bioadsorbent, treated by the explosion technique and impregnated with surfactants. The samples were characterized through compositional analysis, SEM, DRX, FRX and FTIR. The effects of initial metal concentration (20 – 50 mg L-1), pH (2 – 6), mass of adsorbent (0.25 – 1.0g), contact time (10 – 480 min) and temperature ( 10 – 40o C) were studied, in batch mode, with a speed of 100 rpm. To treat the batch results, thermodynamic studies of adsorption and kinetic isotherms were carried out under optimal operating conditions. The results appreciated that the maximum adsorption capacity was higher (28.36 mg g-1) for elephant grass modified simultaneously by steam explosion and surfactant impregnation (CEET). The thermodynamic study showed that the adsorption process is not spontaneous and that the adsorption is exothermic and chemical in nature, as well as high rates of adsorption by chromium ions. The Langmuir model fitted better to the experimental points for all adsorbents, except for the CE adsorbent, which fitted better to the Freundlich model. In kinetic terms, the adsorption of Cr (III) followed a Pseudo Second Order model. A dynamic study in a fixed bed was performed with the CEET adsorbent using a metallic solution feed rate of 300 mL min-1 and an adsorbent mass of 6 g. The rupture curve, the adsorption capacity of the adsorbent by the metal (85.35 mg g-1) and the estimation of the parameters: effective diffusivity (Def), axial diffusion (DL) and external transfer efficiency (ks) were reached from the mass balance performed in the liquid and solid phases. The model elaborated from the balance sheets satisfactorily adjusted to the experimental points. The obtained results can be affirmed that the techniques of treatment and modified of the bioadsorbent improved its capacity of adsorption by the metal chromium (III).